Volume changer employing a magnetic responsive resistor and providing a direct or inverse relation of output to input



NOV. 2, 1965 w, AIKEN 3,215,928

VOLUME CHANGER EMPLOYING A MAGNETIC RESPONSIVE RESISTOR AND PROVIDING ADIRECT OR INVERSE RELATION OF OUTPUT TO INPUT Original Filed Dec. 15.1960 /14 P V 10 INPUT 20 MMAGNET0 2 RESISTANCE DEVlCE so i 1 8+ 16 8 1+)F 12 OUTPUT BIAS INVENTOR.

WILLIAM ROSS AIKEN United States Patent C) 3,215,928 VOLUME CHANGEREMPLOYING A MAGNETIC RESPONSIVE RESISTOR AND PROVIDING A DI- RECT ORINVERSE RELATION F OUTPUT T0 INPUT William Ross Aiken, 10410 MagdalenaAve, Los Altos Hills, Calif.

Original application Dec. 15, 1960, Ser. No. 76,014. Divided and thisapplication Feb. 26, 1962, Ser. N 0. 175,612

5 Claims. (Cl. 323-94) This is a division of my US. patent applicationSerial No. 76,014, filed December 15, 1960, and now abandoned.

The present invention relates to circuit arrangements which operate tochange the volume of a desired signal.

The problem of controlling the gain of electronic amplifiers in the faceof variations in the strength of the incoming signal exists in the fieldof audio and radio broadcasting, and more recently also in thetelevision field. Thus, in radio transmission a standard level of signalstrength is obviously desirable from the viewpoint of optimumutilization of the transmitting facilities, and proper control of theoccasional excessive modulation peaks permits a substantial increase inthe signal power; and in audio reproduction appropriate volume controlenables the listener to restore the full contrast present in theoriginal signal, for instance in vocal and instrumental music, which isgenerally reduced by compression at the place of origin.

Most of the methods that have been proposed in the past for controllingthe gain of a signal suffer from one or more serious defects. One suchdefect is that the control voltage may appear in the output of theamplifier and, moreover, may be many times larger than the desiredsignal itself. Some attempts have been made to reduce this undesirableeffect by placing .a limitation on the speed of response of the controloperation so that the frequency of the control voltage lies well belowthe frequency of the signal voltage and may thus be filtered out withrelative ease. Alternatively, push-pull circuits or balanced modulatorcircuits have been used to cancel out the control voltage in theamplifier output. However, such remedies may restrict the controlcircuits to relatively low speeds of response. Moreover, it is usuallynecessary to operate amplifiers of this type at very low volume levelsto maintain distortion within tolerable limits. Thus, previouslyproposed gain control system-s have been slow in operation, restrictedin band width, delicate in balance, and subject to considerabledistortion.

It is an object of the invention to provide a volume changer thatsuffers from none of these difficulties.

More specifically it is an object of the invention to provide a rapidlyresponsive automatic volume changer arrangement which does not distortthe signal as it changes its volume.

Still another object of the invention is to provide an automatic volumechanger arrangement which does not introduce control voltages into thecontrolled signal so that only the desired signal appears in the outputof the volume changer arrangement.

These and other objects of my invention will be apparent from thefollowing description of the accompanying drawing which shows a circuitdiagram of a preferred embodiment of an automatic volume changerarrangement embodying my invention.

The arrangement illustrate-d in the drawing comprises a pair ofresistors and 12 that are connected in series between the input means 14of the arrangement and ground, and a portion of the signal voltagedeveloped across these resistors is taken off at a point 16 between saidresistors and appears in the output line 18. The

3,2l5,928 Patented Nov. 2, 1965 size of the signal voltage appearing inthe output line depends upon the relative value of the twoseries-connected resistors and will be large if resistor 12 is large ascompared with resistor 10 or small if the resistor 12 is small ascompared with resistor 10. Hence, by making one or the other of saidresistors variable, it is possible to increase or decrease the relativesize of the signal output in line 18 at will. In the exemplaryembodiment of the invention illustrated in the drawing, the upperresistor 10 is made variable and in accordance with my invention it isformed by a magneto-resistance device. Such devices are made of the samematerials as polycrystalline Hall generators and are of low resistancein the absence of a magnetic field, but their resistance may beincreased by factors ranging from 25 to 50 when placed into a magneticfield. In accordance with the invent-ion, therefore, I arrange adjacentthe magneto-resistance device 10 a ma gnetizing coil 20, and themagnetic field generated by said coil and hence the resistance value ofthe device 10 is controlled by the strength of the signal that passe-sthrough the arrangement. If the arrangement is to operate as a volumeexpander, the energization of coil 20 may be controlled by a negativevoltage which is derived from the signal at the input end of thearrangement in such a manner that en-ergization of the coil 20 isreduced as the volume level of the incoming signal increases and isintensified as the volume level of said signal decreases so that thevalue of magneto-resistance device 10 decreases with increasing volumelevel and increases with decreasing volume level. This causes thevoltage appearing in the output line 1-8 to increase as the volume levelof the signal increases and to decrease as the volume level of thesignal decreases.

Having again reference to the drawing, a part of the incoming signalvoltage is rectified at 22 and the negative component thereof is appliedthrough a suitable filter network collectively identified by thereference numeral 24 to the control grid 26 of a tube 28 in whose anodecircuit the magnetizing coil 20 is located. Hence, as the negativecontrol voltage applied to the grid of the tube 28 increases, lesscurrent flows in the anode circuit of said tube and the magnetic fieldgenerated by the coil 20, therefore, decreases. This causes the resistor10 to decrease in value and the voltage in line 18 to increase in size;and vice versa, when the volume level of the incoming signal decreases,the negative bias applied to the control grid of the tube 28 decreasesand causes more current to flow in the anode circuit thereof. As aresult thereof, the magnetic field generated by coil 20 increases inintensity which causes the value of the variable resistor 10 to increaseand reduce the voltage of the signal appearing in output line 1 8.

To operate the described arrangement as a volume compressor a part ofthe signal voltage appearing in the output line 18 may be rectified at30, and the positive component thereof be supplied through the filternetwork 24 to the control grid 26 of the tube 28 causing said grid tobecome more positive as the volume level of the output signal increases.This increases the current flow in the anode circuit of the tube 28 andas a result thereof the magnetic field generated by coil 20 increases inintensity, which causes the resistance of the magnetic resistance device10 to increase. Thus, with increasing volume level of the output signal,the arrangement operates to reduce the volume level of the outputsignal; and vice versa, as the volume level of the signal appearing inthe output line 18 decreases, less positive bias is applied to the gridof the tube 28, less current flows through the coil 20 and theresistance of device 10 decreases causing a greater portion of thevoltage to appear in. output line 18.

In the particular embodiment of the invention illustrated in thedrawing, the volume changer arrangement may readily be set to operate asan expander or compressor by manipulation of a suitable switch 32 whichsupplies the grid of the tube 28 with a negative control voltage derivedfrom the input side of the arrangement when in the position shown infull lines, and with a positive control voltage derived from the outputline of the arrangement When in the position Shown in broken lines. Atthe same time it is, of course, necessary to change appropriately the.initial bias applied to the control grid of the tube 28. It will beunderstood by those skilled in the art that a volume expanderarrangement may also be constructed to derive its control voltage fromthe output side of the volume changer, and vice versa, 21 volumecompressor arrangement may also be constructed to derive its controlvoltage from the input side of the volume changer. Furthermore, anexternal source of control voltage may be employed to exercise remotecontrol over the arrangement :of the invention and/or control thearrangement according to a predetermined program.

The automatic volume control arrangement of my invention is of simpleconstruction, yet operates fast and dependably. Since themagneto-resistance device does not by itself produce a voltage, nocontrol voltages are int-roduced into the signal, that might appear inthe output line of the volume changer and distort the desired signal orproduce background noises.

It is Within the scope of my invention to modify the arrangementillustrated in the drawing by using a magneticresistance device forresistor 12 and employing an ordinary resistor in place of the device10. In such an arrangement it is necessary, however, to control the flowof current through the magnetizing coil 20 with a positive voltage ifthe arrangement is to operate as an expander, and to control the flow ofcurrent through the coil 20 with a negative voltage if the arrangementis to operate as a compressor.

While I have explained by invention with the aid of a preferredembodiment thereof, it will be understood that the invention is notlimited to the specific circuit arrange ment shown and described by wayof example, which may be departed from without departing from the scopeand spirit of the invention.

I claim:

1. A volume changer arrangement comprising alternating signal inputmeans, a pair of resistors connected in series between, said signalinput means and ground, at least one or" said resistors being amagneto-resistance device having a resistance value that varies inresponse to magnetic fields, means for establishing a magnetic fieldadjacent said magneto-resistance device, and. means for controlling theintensity of the magnetic field established by said field-establishingmeans with a voltage derived from the input signal passing through thevolume changer arrangement.

2. A volume changer arrangement comprising signal input means, aresistor variable in response to magnetic fields and a fixed resistorconnected in series between said input means and ground, signal outputmeans connected to a point intermediately of said resistors, amagnetizing coil arranged adjacent said variable resistor, means forenergizing said magnetizing coil, and means for controlling theintensi-ty of the magnetic field established by said magnetizing coilwith a voltage derived at said input means from the signal passedthrough said volume changer.

3. A volume changer arrangement comprising signal input means, aresistor variable in response to magnetic fields and a fixed resistorconnected in series between said signal input means and ground, signaloutput means connected to a point intermediately of said resistors,means for establishing a magnetic field arranged adjacent said variableresistor, and means for controlling the degree of energization of saidfield-establishing means with a voltage derived at said signal outputmeans from the signal passed through the volume changer arrangement.

4. A volume changer arrangement comprising alternating signal inputmeans, a resistor variable in response to magnetic fields and a fixedresist-or connected in series between said signal input means andground, signal output means connected to a point intermediately of saidresistors, means for establishing .a magnetic field arranged adjacentsaid variable resistor, and means for controlling the degree ofenergization of said field-establishing means in inverse relation to thevolume strength of the signal passing through said arrangement With avoltage derived from the input signal passing through said arrangement.

5. A volume changer arrangement comprising signal input means, aresistor variable in response to magnetic fields and a fixed resistorconnected in series between said signal input means and ground, signaloutput means connected to a point intermediately of said resistors,means for establishing a magnetic field arranged adjacent said variableresistor, and means for controlling the degree of energization of saidfield-establishing means in direct relation to the volume strength ofthe signal passing through said arrangement with a voltage derived fromthe signal passing through said arrangement.

References Cited by the Examiner UNITED STATES PATENTS 2,549,775 4/51Charchian 33832 2,752,434 6/56 Dunlap 338-32 2,979,668 4/61 Dunlap '330-6'2 3,082,381 3/63 Morrill et al 3 30-59 3,086,126 4/63 Dunlap30788.5

FOREIGN PATENTS 1, 181,706 6/59 France.

848,369 9/60 Great Britain.

LLOYD MCCOLLUM, Primary Examiner,

1. A VOLUME CHANGER ARRANGEMENT COMPRISING ALTERNATING SIGNAL INPUTMEANS, A PAIR OF RESISTORS CONNECTED IN SERIES BETWEEN SAID SIGNAL INPUTMEANS AND GROUND, AT LEAST ONE OF SAID RESISTORS BEING AMAGNETO-RESISTANCE DEVICE HAVING A RESISTANCE VALUE THAT VARIES INRESPONSE TO MAGNETIC FIELDS, MEANS FOR ESTABLISHING A MAGNETIC FIELDADJACENT SAID MAGNETO-RESISTANCE DEVICE, AND MEANS FOR CONTROLLING THEINTENSITY OF THE MAGNETIC FIELD ESTABLISHED BY SAID FIELD-ESTABLISHINGMENS WITH A VOLTAGE DERIVED FROM THE INUT SIGNAL PASSING THROUGH THEVOLUME CHANGER ARRANGEMENT.